The invention concerns recombinant antibodies binding to prostate-specific stem cell antigen (PSCA) and their use in diagnostics and therapy. The antibodies are suitable for use in the field of medicine, pharmacy and biomedical research.
Prostate carcinoma is one of the most frequent cancer-related causes of death in Germany. The standard therapy for a primary, organ-limited prostate carcinoma is currently radical prostatectomy, i.e. the complete removal of the prostate, seminal vesicles, and lymph nodes. An alternative to this is radiotherapy which is done by spiking the prostate with radioactive material (brachytherapy). Most patients with primary, local prostate carcinoma can be treated successfully by radical prostatectomy and radiotherapy. A relapse occurs in about 20-40% of the affected persons [Roehl 2004].
Presently, different antibody-based therapy procedures are being developed. In this context, it is of essential importance to identify target structures on the cancer cells which can serve as sites of attack for the antibody-based therapeutics. A suitable target structure as an attack site for the treatment of prostate cancer are surface proteins which are present primarily in the prostate tissue and which exhibit overexpression in malignant cells in comparison to healthy cells.
The prostate-specific stem cell antigen (PSCA) is such a surface molecule which is present specifically on prostate cells and is expressed at a higher rate in prostate carcinoma cells in comparison to healthy tissue (tumor-associated antigen). Human PSCA comprises 123 amino acids and has an N-terminal signal sequence, a C-terminal glycosylphosphatidylinositol (GPI) anchoring sequence and several N-glycosylation sites. PSCA is included in the Thy-1/Ly-6 family of the GPI-anchored cell surface molecules because, inter alia, it has the characteristic preserved cysteine residues of this family [Reiter 1998].
On account of the increased expression in prostate tumors, PSCA is a suitable target molecule for the therapy of prostate cancer and, up to now, different therapy strategies which are aimed at PSCA as a target have been developed. Evidence of the efficacy of PSCA as a therapeutic target in cancer therapy on human subjects has been produced, inter alia, by vaccination with dendritic cells which were loaded before with a PSCA peptide. Clinical studies (phase 1 and 2) with 12 hormone-refractory and chemotherapy-refractory prostate cancer patients have demonstrated that a vaccination with PSCA peptide-loaded dendritic cells caused a T-cell response against PSCA which correlated on average with an extended survival rate in five of the patients. In one patient even a reduction of the tumor mass was observed [Thomas-Kaskel 2006].
WO 2009/032949 A2 discloses monoclonal anti-PSCA antibodies (1G8) which are used for targeting tumors and for their detection. The CDR regions of the antibodies have the following amino acid sequences:
variable region of the light chainvariable region of the (1G8)heavy chain (1G8)CDR1SASSSVRFIHWSEQ ID DYYIHWSEQ IDNo. 69No. 72 CDR2DTSKLASSEQ ID WIDPENGDTEFVPKFQGSEQ IDNo. 70No. 73 CDR3QQWSSSPFTSEQ ID TGGFSEQ IDNo. 71No. 74
On account of the cytotoxic properties of the 1G8 antibody, the latter is unsuited for targeting strategies which are based on the recruitment of effector cells (Gu 2005).
The antibodies disclosed in WO 2009/032949 A2 are used diagnostically preferably in the form of functional murine and humanized monoclonal antibodies as well as PSCA-specific minibodies and diabodies marked with radionuclides.
[Feldmann 2010] have developed bispecific recombinant antibodies with a PSCA-binding paratope and a CD3-binding paratope. The PSCA-binding paratope of the bispecific antibodies is derived from the PSCA antibody 7F5 [Morgenroth 2007] and comprises CDR regions with the following amino acid sequences:
variable region ofthe light chainvariable region of the(7F5)heavy chain (7F5)CDR1RTSQDISNYLNSEQ IDSYTMSSEQ IDNo. 27No. 30 CDR2YTLKLNSSEQ IDYIHNGGGHTYYPDTIKGSEQ IDNo. 28No. 31 CDR3QQSKTLPWTSEQ IDRMYYGNSHWYFDVSEQ IDNo. 29No. 32
The bispecific antibodies disclosed in [Feldmann 2010] in vitro successfully caused the specific T-cell mediated lysis of PSCA-positive tumor cells. For a specific lysis of about 40% of the employed PSCA-positive tumor cells, for a ratio of effector cells to PSCA-positive tumor cells of 20:1 at least 5 ng of the bispecific antibody disclosed in [Feldmann 2010] is to be used. In vitro, a specific lysis of maximally about 60% of the employed PSCA-positive tumor cells (in the presence of 50-100 ng of the antibody) has been achieved with the antibodies disclosed in [Feldmann 2010]. A further increase of the effectiveness could not be proved. Even in the presence of 1,000 ng of the bispecific antibody, a higher proportion of PSCA-positive tumor cells could not be lysed.
The known in vitro and in vivo data show that PSCA has a great potential as a target antigen for the immunotherapy of prostate carcinomas and is suitable as a diagnostic target.
The object of the invention is to provide improved antibodies against PSCA which are therapeutically effective in particular in the form of bispecific recombinant antibodies in low concentration and are able to lyse PSCA-positive tumor cells effectively.